Roughly 4 million adult children provide unpaid care to their parents with Alzheimer's disease and related dementias (ADRD). Caring for a parent with ADRD can be stressful and negatively impact caregivers' health. While research on spousal caregiving dyads shows that emotionally supportive communication between spouses in the early stages of ADRD can protect caregivers' health, little is known about such interpersonal processes in parent-child dyads. This needs to be addressed because adult child caregivers and their parents face different interpersonal challenges (e.g., navigating a reversal of the parent-child role) than spousal dyads. We have shown in our spousal caregiving work that mutual emotional support behaviors, defined as caregivers and care-recipients providing and receiving communication of safety, feeling comfortable expressing vulnerability and empathy, and giving and receiving tangible aid, decrease caregiving burden and protect psychological health. Mutual emotional support behaviors are amenable to change, making them appropriate targets for interventions. Our research is informed by attachment theory, which stipulates that the need for emotional security is a fundamental need in the parent-child dyad across the lifespan, especially in times of crisis. Our overarching hypothesis is that mutual emotional support behaviors can protect the health of adult child caregivers and parents by reducing caregiver stress and negative coping strategies. We integrate our hypotheses about mutual support into an existing dyadic caregiving stress model that shows how caregiver and care-recipient characteristics, primary and secondary stressors, caregiver appraisals and coping all influence both dyad members' health and relational functioning. To test our innovative model, we propose a Stage 0 dyadic, longitudinal, and observational study of 200 dyads: older adults aged 60 and older with early stage ADRD and one primary adult child caregiver. Both dyad members will be interviewed, using valid and reliable self-report measures, and have videotaped discussions about dementia-related stressors at baseline and a one-year follow-up. Mutual emotional support behaviors will be measured with an observational coding system created by Co-I Feeney, and blood pressure will be monitored. Dyadic analysis will be performed with mixed models and structural equation modeling. Aim 1 will examine whether mutual emotional support behaviors are associated with lower caregiver demand appraisals, caregiver perceived stress, and caregiver negative coping longitudinally. Aim 2 will examine whether mutual emotional support behaviors protect both dyad members' health and relational functioning longitudinally and whether this is mediated by lower caregiver demand appraisals, caregiver perceived stress, and caregiver negative coping. Aim 3 will examine mutual emotional support behavior differences by sex as a biological variable and contextual factors (e.g., SES, caregiver depression, relationship history). This will lead to a Stage 1 application to create an attachment- based intervention tool to protect the health of parents with ADRD and their adult child primary caregivers.